This invention relates to apparatus for generating an extremely high pressure shock wave in a liquid medium by means of a pulsed plasma established therein.
The presence of an electrical discharge between electrodes immersed in a liquid-like medium is known to produce a "spark channel" between the electrodes. The spark channel ionizes the adjacent liquid to create a plasma therein. Among other effects, the plasma results in the production of ultrahydraulic pressure and ultraviolet radiation effects in the surrounding liquid medium. These effects have been used in a variety of ways to treat liquid-like substances in a confined environment in order to purify the liquid. One process described in U.S. Pat. No. 4,458,153 utilizes the effects of a spark discharge produced between electrodes in combination with a localized magnetic field to alter the characteristics of confined liquid substances.
On a laboratory scale, limited volumes of liquid-like substances have been treated in relatively small, confinement chambers, for example less than one liter, wherein a spark discharge is established for a brief period. While the use of small confinement chambers in combination with relatively low power sparks is useful for some small batch processing utilizing the generated radiation and the pressure effects, the extension of the length of the spark channel and impedance matching of the electrical driver network to that of the spark channel to create a larger plasma volume and energy density is a desirable goal. The application of increased power to the spaced electrodes in the chamber creates an opportunity to increase the length of the spark channel while maintaining a high energy density in the plasma. In addition, chamber design has been found to enhance the generated effects. These conditions enable the beneficial effects of the process to be applied to the treatment of larger volumes of material supplied to the confinement chamber on a continuing basis. One such apparatus for utilizing the effects of a spark channel and the created plasma to purify liquid in a continuing manner is described in my co-pending U.S. application Ser. No. 08/011,224 entitled Apparatus For Treating A Confined Liquid By Means Of A Pulse Electrical Discharge. This novel apparatus utilizes a confining vessel of unique design to increase the beneficial results obtained from a spark discharge and the resultant plasma. The invention disclosed therein permits the use of relatively large chambers having a liquid or slurry passing therethrough on a continuing basis.
Apparatus previously used to gain the benefit of the electrical characteristics of the spark channel and resultant plasma have employed a completely bounded confinement vessel for the medium. This requires fluid transfer to and from the treatment chamber in synchronism with the application of power to the electrodes in the confinement chamber thereby limiting the industrial application of the process and the potential uses of the structure. In this type of operation, the pulsed plasma created between electrodes in the confinement vessel generates an extremely high pressure shock wave in the confined liquid. However due to the fact that the vessel is bounded on all sides, the beneficial effects are experienced only by the limited volume of material contained within the vessel at the time of the creation of the plasma. In order to more hilly utilize the beneficial effects created by a spark channel and resultant shock waves more distant from the spark source, it is necessary to transfer increased amounts of energy in a pulsed form to the apparatus. In addition, it is important to facilitate the transfer of this energy to the plasma to provide high energy effects in the liquid medium. Furthermore, in order for the shock wave created by the formation of the plasma to have a beneficial impact at a distance from the electrodes, a different approach is needed for the geometrical design of the shock wave launching means so as to permit high energy discharges on a repetitive basis. Repetitive high energy pulses carry the benefits resulting from the establishment of shock waves beyond the immediate vicinity of the electrodes.
Accordingly, the present invention is directed to the provision of apparatus for generating an extremely high pressure shock wave by the use of a pulsed plasma in a liquid medium without requiring a bounded vessel for the liquid. The present invention produces the high pressure shock wave in a liquid environment in a manner which enables the beneficial effects thereof to be utilized at a distance from the electrodes. In particular, the effects produced by the pulsed plasma established by the present apparatus can be utilized for the removal of biofouling and scaling from a wide variety of pipes and other structures either containing or exposed to liquids, as well as preventing or inhibiting regrowth or rescaling in these pipes or structures. In addition, the ability to create a shock wave of sufficient magnitude to enable the effects produced by the shock wave to be felt and experienced by objects outside the spark vessel enable the present apparatus to be used to fracture nearby solid substances, such as packed ice and floating ice. The shock wave produced by the present apparatus can also be used to prevent intrusion in water bodies by a wide variety of life forms which would otherwise contaminate ducts, harbors and subpens.
Therefore, it is a primary objective of this invention to provide apparatus for generating, focusing and concentrating shock waves in liquid-like substances which are not confined within the vessel in which the plasma is created. Another objective is to create a plasma between electrodes which is substantially higher in energy density and peak power over those obtained by apparatus heretofore utilized. Furthermore, the present invention enables the applied power pulse to be efficiently utilized in the creation of the plasma. The energy transfer between a pulse forming network and the plasma is enhanced. As a result of enhancement of the peak plasma pumping power employed in the shock wave launching means of the present apparatus, the beneficial effects of the shock wave can be utilized at a distance outside the shock wave launching apparatus.
Also, the present apparatus is configured to permit repetitive generation of high pressure shock waves without unduly shortening the life of the electrodes. The region in which the shock waves are launched is contoured to provide reflection and concentration of the shock waves as they are travelling from the electrodes. This feature enables the effects from the present apparatus to be utilized on large volume structures and on masses located at distances of hundreds of feet from the shock wave launching source. While the present invention is constructed to utilize high energy plasmas, it is to be noted that low level shock waves can be launched thereby at regular intervals as well.